This invention relates to an improved packing gland assembly for providing a gas-tight seal at the point where a damper blade shaft passes through the damper frame of a movable blade damper.
One type of damper known to the art utilizes a peripheral frame which surrounds several movable damper blades. Each of the blades is mounted on a respective shaft which passes through the damper frame, and the shafts are rotated in coordination so as selectively to close and open the damper.
In the past, packing glands have been used around the damper blade shafts to provide a gas-tight seal at the point where the blade shafts pass through the damper frame. One commonly used approach of the prior art is to weld individual packing glands in place on the damper frame to prevent gas leakage such as flue gas leakage around the damper blade shaft.
Though this prior art approach can, if properly implemented, provide a suitable seal around the damper blade shaft, it provides a number of important disadvantages. Once the packing gland has been welded into place on the damper frame, no lateral adjustment can be made of the blade shaft without affecting the concentricity between the blade shaft and the packing gland. Excessive eccentricity between the blade shaft and the packing gland can cause unacceptably high rates of gas leakage through the packing gland. Thus, prior art packing glands which are welded in place to the damper frame can restrict the amount of lateral adjustment that can be made to the blade shafts without physically removing the packing gland. If the blade shafts are not adjusted properly, openings between sealing surfaces on the blades caused by the inability to adjust the blade clearances as desired can also allow unacceptably high rates of gas leakage through the damper when in the closed position.
Furthermore, when packing glands are welded in place to damper frames, replacement of the packing material within the packing gland can be a difficult operation since the gland is open at one end only. In addition, surfaces of the blade shaft within the packing gland are relatively inaccessible due to the fixed location of the gland. Any shaft surface defects in the region of the gland may promote gas leakage through the gland or increase torque requirements to rotate the shaft. Such surface defects can be difficult to detect or correct because they are concealed by the gland. Moreover, packing glands which are welded in place are difficult or impossible to replace due to the need to cut or burn them out.